The group H antigen has bee found to be a glycerol teichoic acid found in m ost strains of Streptococcus sanguis tested. The antigenic determinant appears to be a beta 1,6 diglucosyl glucoside and thus is immunochemically distinct from the type specific b antigen which contains an alpha 1,6 diglucosyl glucoside as a determinant. Both these polymers are found in the cell walls of S. sanguis. The teichoic acid in the group anitgen appears to represent only 15% of the weight of the antigen, the remainder appears to be a heteropolymer consisting of rhamnose, glucose and galactose. Purification of the cell wall teichoic acids on Sapharose yields two serologically active fractions: a small amount of relatively high molecular weight antigen containing lipid and giving a possible hemagglutination test with either anti-teichoic acid serum or group specific antiserum; a low molecular weight deacylated teichoic acid which does not hemagglutinate is the major serologically active component. Attempts to obtain large quantities of the group antigen using the spent medium as a starting material was unsuccessful because the amount of teichoic acid was only 0.2% of cell dry weight. This observation suggest the teichoic acids in S . sanguis may not be secreted as in other streptococci but merely results from autolysis of a small number of cells. The teichoic acids found in the spent medium are both acylated and deacylated. Strains identified as S. mitis contain no glycerol teichoic acids either in membrane, wall or in the spent medium. No group antigen has yet been identified for these organisms using the standard antigen extraction method, e.g., phenol-water, Rantz and Randall, sonication and Lancefield. Attempts are being made to obtain and compare extracts obtained by enzymatic lysis of the cells to determine if a common backbone polymer is present in these organisms. If found, it may be possible to modify the polymer and make antibody against the backbone to use as a grouping antigen. The importance of grouping is seen in comparing adherence of oral streptococci to salivary coated gydroxyapatite, a model for plaque fromation. In these studies three distinct types of adherence to hydroxyapatite were detected. These interactions were correlated with the subtypes of S. sanguis.